Duration of protection against vibriosis in ayu Plecoglossus altivelis vaccinated by immersion and oral administration with Vibrio anguillarum.

Excellent protection against vibriosis was provided to ayu Plecoglossus altivelis vaccinated by immersion with 5.32% NaCl solution containing either 0.94 (wet)g/l or 9.4 (wet)g/l of lyophilized cells of Vibrio anguillarum. The duration of protective immunity in fish was at least 113 days. A high level of protection against vibriosis was also demonstrated in fish orally vaccinated with bacterin administered at a rate of 0.94 (wet)g/kg fish/day for 15 days. However, this protective immunity lasted only 50 days after the first administration of vaccine. The serum from fish which had been vaccinated by either the immersion or oral administration did not show detectable levels of agglutinating antibodies against V. anguillarum.